Seals are generally used for sealing connections of flanges, for example that are typically used in the chemical, petrochemical or pharmaceutical industries and in power plants. Sealing elements are always necessary when there is unevenness in the opposite sealing faces of at least one of the flanges involved, which is often the case.
The purpose of such a sealing element is that it undergoes plastic, elastoplastic or elastic deformation during assembly such that any existing unevenness in the at least one sealing face is compensated for. For this reason, a sealing element is often made of a softer material than the flange material.
It is problematic that considerable unevenness in at least one sealing face of the flanges involved or the total of unevenness in the two sealing faces involved can no longer be compensated for by traditional seals, in particular when such unevenness amounts to more than 10 mm.
Such considerable unevenness can occur due to strong thermal loads in the flange-making process, for example, in particular when the flanges are made of steel and have an enamel coating, for example, in order to achieve a chemical resistance.
Applying the enamel coating requires high-temperature heating of the parts to be enameled and therefore also the flanges, so there may be considerable deformation of the parts and thus also the flanges, so that even a sealing face of a flange that was originally made flat, for example, may have a substantial unevenness, for example, greater than 10 mm, after application of the enamel layer.
When such considerable unevenness occurred in the past, it has been necessary to repeat the enameling process for lack of availability of suitable seals. To do so, the old layer of enamel has to be removed, and if necessary the sealing faces would be smoothed and recoated.
However, unevenness of this magnitude can occur not only when there is a thermal load on the flanges, but also due to aging effects, for example, and the resulting distortion of the flanges or parts adjacent them.